1. Field of the Invention
The present invention relates to an electric motor, and more particularly, to a rotor of an electric motor that has a simplified structure and is improved so as to accurately detect a position of the rotor, and an electric motor having such a rotor.
2. Description of the Background Art
In general, an electric motor has a housing, a stator provided in the housing and having a coil wound thereon, a rotary shaft supported to the housing so as to be rotatable, and a rotor having the rotary shaft pressingly inserted and fixed to the center thereof, the rotor moving by electromagnetic interaction with the stator.
In addition, a plurality of pairs of permanent magnets having magnetic poles opposite to each other are inserted into the rotor in a direction of the rotary axis of the rotor. Magnetic flux of the magnets is linked through the coil of the stator so as to generate rotating torque that rotates the rotor.
Here, a control unit needs to detect a position of the rotor in order to continuously drive the rotor and control rotative velocity of the rotor. When detecting the position of the rotor, the control unit controls a current, which is applied to the stator, on the basis of the position of the rotor, so as to continuously drive the rotor or control the rotative velocity of the rotor.
In general, in order to detect the position of the rotor, a sensor magnet is separately provided at the rotary shaft, and a hall sensor is provided to be adjacent to the sensor magnet.
The hall sensor senses changes in magnetic flux that are made by the sensor magnet by rotation of the rotary shaft, and converts the changes in the magnetic flux into an electrical signal. The converted electrical signal is transmitted to the control unit. The control unit controls a current, which is applied to the stator, according to the transmitted signal. At this time, the sensor magnet needs to be provided at an accurate position that corresponds to magnetic poles of the permanent magnets that are inserted into the rotor.
However, an assembly error may occur in a process of assembling the sensor magnet. When the assembly error exceeds the maximum permissible limit, an error with respect to the detected position of the rotor increases, and thus, an error in controlling the rotation of the rotor correspondingly occurs.
In addition, since a process of magnetizing the sensor magnet and a process of assembling the sensor magnet so as to be provided at the rotary shaft are needed, there is a limitation on simplification of an assembly process.
Recently, a permanent magnet type synchronous reluctance motor having permanent magnets inserted into flux barriers has been used, but this type of motor has the same problems.